This invention relates to the measurement of relative oxygen saturation of choroidal blood of the eye fundus, and more particularly to such measurements in specifically selected areas of the eyegrounds.
Recent evidence, obtained by means of special infrared photographic techniques, has demonstrated an important distinctiveness of the blood capillary distribution of the two most critical areas of the posterior pole fundus eyegrounds. These are the peripapillary area adjacent to, and surrounding the optic nerve head and the macular area which is the center of vision for form and color. These areas are critically important to vision because they are involved in the two leading causes of blindness; namely, glaucoma and macular degeneration. The recent infrared photographic evidence has shown that the capillary blood (choriocapillaris) in these two areas diminishes and ultimately disappears with progression of the diseases of glaucoma and macular degeneration. Fortunately, these two causes of blindness rarely occur together in the same individual. However, early diagnostics could improve the prognoses of these diseases by reason of the consequent earlier and therefore more effective treatment.
A successful method and instrumentation for measuring the relative oxygen saturation of the choroidal blood of the eye fundus is disclosed by Laing et al in IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, Volume BME-22, No. 3, May 1975, Pages 183-195, entitled THE CHOROIDAL EYE OXIMETER: AN INSTRUMENT FOR MEASURING OXYGEN SATURATION OF CHOROIDAL BLOOD IN VIVO. In this disclosure, only fields of view of the eyegrounds which were larger than 10.degree. were used. However, such large spectral sampling areas are too large to separate the two critically important areas; namely, the macula and peripapillary. Moreover, the instrumentation is so large, heavy and non-portable that its use is limited. Moreover, the large angle of the field of view renders the method and instrumentation inefficient since it is essential to be able to study accurately either the optic disc or the macula without overlapping by the other.